Percussion drill bit with conical cutting elements

ABSTRACT

A percussion drill bit for drilling a borehole. The drill bit includes a bit body having a bit face disposed on an axial end portion thereof. First and second cutting elements are disposed on the bit face. A cutting plane is defined in tangential contact with crest portion of the first and second cutting elements. A third cutting element on the bit face is at least partially positioned between the first and second cutting elements. The third cutting element is at least partially conical, and a crest portion of the third cutting element is offset from the cutting plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of, and priority to, U.S. Patent Application No. 61/746,765, filed on Dec. 28, 2012 and entitled “PERCUSSION DRILL BIT WITH CONICAL CUTTING ELEMENTS,” which application is expressly incorporated herein by this reference in its entirety.

BACKGROUND

In drilling a borehole in the earth—such as for the recovery of hydrocarbons or for other applications—a drill bit may be connected to the lower end of a drill string that includes a plurality of end-to-end connected drill pipe sections. The drill bit is rotated by rotating the drill string at the surface and/or by actuation of downhole motors or turbines. With weight applied to the drill string, the rotating drill bit engages the earthen formation causing the drill bit to cut through the formation material by either abrasion, fracturing, or shearing action, thereby forming the borehole.

There are several types of drill bits which may be used, including percussion hammer bits, roller cone bits, fixed cutter bits, and drag bits. In percussion hammer drilling operations, the drill bit may be mounted to the lower end of the drill string, and the drill string may move the drill bit back and forth axially to impact the earth to crush, break, and loosen formation material. To promote efficient penetration, the percussion hammer drill bit may be “indexed” to fresh earthen formations for each subsequent impact. Indexing is achieved by rotating the percussion hammer drill bit between each axial impact of the bit with the earth. In such operations, the mechanism for penetrating the earthen formation is of an impacting nature, rather than shearing. The impacting and rotating percussion hammer drill bit engages the earthen formation and proceeds to form the borehole along a path and toward a target zone.

The cost of drilling a borehole may be proportional to the length of time it takes to drill the borehole to the desired depth and location. The drilling time, in turn, is greatly affected by the number of times the drill bit is changed in order to reach the desired depth and location. This is the case because each time the drill bit is changed, the entire drill string—which may be miles long—is retrieved and each removed from the borehole. Once the drill string has been retrieved and removed, and the new drill bit installed, the drill bit is lowered to the bottom of the borehole on the drill string, which is again constructed by securing each drill string section end-to-end with an adjacent drill string section. This process, known as a trip of the drill string, entails considerable time, effort, and expense.

SUMMARY

Embodiments disclosed herein generally relate to cutting elements. More particularly, embodiments of the present disclosure relate to cutting elements for percussion hammer drill bits. More specifically still, some embodiments disclosed herein relate to conical cutting elements for percussion hammer drill bits.

A percussion drill bit for drilling a borehole is disclosed. The drill bit includes a bit body having a bit face. First and second cutting elements are positioned on the bit face and definine a cutting plane. The cutting plane is in tangential contact with crest portions of each of the first and second cutting elements. A third cutting element on the bit face is a conical cutting element and is at least partially between the first and second cutting elements. The conical cutting element includes a crest portion offset from the cutting plane.

In another embodiment, a percussion drill bit includes a bit body having a bit face. First and second semi-round cutting elements positioned in an outer circumferential row on the bit face, and define a cutting plane. The cutting plane is in tangential contact with crest portions of the first and second cutting elements. A third cutting element on the bit face at least partially overlaps the outer circumferential row and is at least partially conical. A crest portion of the third, conical cutting element extends beyond the cutting plane by a distance up to about 70% of a total height of the third cutting element as measured from the bit face.

A method for drilling a borehole is disclosed. The method includes running a percussion hammer drill bit into a borehole. The percussion drill bit includes a bit body having a bit face with first, second, and third cutting elements thereon. A cutting plane is defined in tangential contact with crest portions of the first and second cutting elements. The third cutting element is positioned at least partially between the first and second cutting elements, is at least partially conical, and has a crest portion that is offset from the cutting plane. The first, second, and third cutting elements contact a formation to extend the borehole.

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A depicts a perspective view of an illustrative percussion hammer drill bit, according to one or more embodiments of the present disclosure.

FIG. 1B depicts a top view of the percussion hammer drill bit shown in FIG. 1A, according to one or more embodiments of the present disclosure.

FIG. 2A depicts a profile view of a portion of the percussion hammer drill bit, according to one or more embodiments of the present disclosure.

FIG. 2B depicts an enlarged, partial profile view of the percussion hammer drill bit shown in FIG. 2A, according to one or more embodiments of the present disclosure.

FIGS. 2C and 2D depict enlarged, partial profile views of the percussion hammer drill bit shown in FIG. 2B, according to one or more embodiments of the present disclosure.

FIG. 3A depicts a profile view of a portion of a percussion hammer drill bit, according to one or more embodiments of the present disclosure.

FIG. 3B depicts an enlarged, partial profile view of the percussion hammer drill bit shown in FIG. 3A, according to one or more embodiments of the present disclosure.

FIG. 4A depicts a profile view of a portion of a percussion hammer dull according to one or more embodiments of the present disclosure.

FIG. 4B depicts an enlarged, partial profile view of the percussion hammer drill bit shown in FIG. 4A, according to one or more embodiments of the present disclosure.

FIG. 5A depicts a profile view of a portion of a percussion hammer drill bit, according to one or more embodiments of the present disclosure.

FIG. 5B depicts an enlarged, partial profile view of the percussion hammer drill bit shown in FIG. 5A, according to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

FIGS. 1 and 2 depict perspective and top views, respectively, of an illustrative percussion hammer drill bit 100, according to one or more embodiments of the present disclosure. The percussion hammer drill bit 100 includes a bit body 102 having a central axis (“bit axis”) 104 extending therethrough. The drill bit 100 may be indexed (i.e., rotated) about the bit axis 104 during drilling operations.

A bit face 106 may be disposed on an axial end portion of the bit body 102. The bit face 106 may include a plurality of inserts or cutting elements 110 disposed thereon. The bit face 106 may include inner and outer regions 112, 114. The inner region 112 may include the radially innermost region of the drill bit 100, and may extend from the bit axis 104 to the outer region 114. The outer region 114 may extend from the inner region 112 to a skirt region 122. Optionally, the skirt region 122 may be about parallel to the bit axis 104.

The outer region 114 may include a circumferential gage row 126 having gage cutting elements 136. In the illustrated embodiment, there is a plurality of gage cutting elements 136. The circumferential gage row 126 may be the outermost radial row on the bit face 106. The gage cutting elements 136 may be circumferentially offset from one another in the gage row. The gage cutting elements 136 may be adapted to cut the corner of the borehole. Stated another way, the gage cutting elements 136 may cut an outermost, or largest radius portion of the borehole bottom and/or borehole sidewall during drill operations. Accordingly, the gage cutting elements 136 may maintain the diameter or gage of the borehole.

The outer region 114 (or potentially the inner region 112) may include a circumferential adjacent-to-gage row 128 having one or more adjacent-to-gage cutting elements 138. A plurality of adjacent-to-gage cutting elements 138 may be circumferentially offset from one another in the adjacent to gave row 128 and positioned radially inward from the gage cutting elements 136 in the gage row 126. The adjacent-to-gage cutting elements 138 may be adapted to cut the bottom of the borehole in some embodiments. As discussed in more detail herein, one or more additional rows 130 of cutting elements 140 may also be positioned radially inward from the adjacent-to-gage row 128 at the inner region 112 or the outer region 114. The one or more additional rows 130 of cutting elements 140 may be adapted to gouge and remove formation material from the bottom of the borehole in some embodiments.

The cutting elements 136, 138, 140 may be semi-round top (“SRT”) cutting elements having a hemispherical shape. A ratio of the radius of curvature of a crest portion of the cutting elements 136, 138, 140 to the diameter of the cutting elements 136, 138, 140 may range from about 0.3:1 to about 1:1. For instance, such a ratio may range from a low of about 0.3:1, about 0.4:1, or about 0.5:1 to a high of about 0.6:1, about 0.7:1, about 0.8:1, or more. For example, the ratio of the radius of curvature to the diameter may be between about 0.4:1 and about 0.7:1. As used herein, “crest portion” refers to the portion of a cutting element that is most distal relative to the bit face 106 (e.g., the tip or apex) and/or the portion of a cutting element that is likely to initially contact the formation during drilling operations.

In at least one embodiment, the cutting elements 110 from different circumferential rows (e.g., rows 126, 128, 130) may be radially offset from one another with little to no overlap. In another embodiment, the cutting elements 110 from one circumferential row may at least partially radially overlap with the cutting elements 110 from a different circumferential row. The degree of radial overlap of the cutting elements 110 in adjacent circumferential rows may be characterized by the ratio of the radial overlap distance to the radial span distance of the overlapping cutting elements. As used herein, “radial overlap distance” refers to the radial distance over which two adjacent cutting elements 110 overlap. “Radial span distance” refers to the radial distance spanned or covered by the two adjacent overlapping cutting elements. Thus, “radial overlap ratio” refers to the ratio of the radial overlap distance to the radial span distance. The radial overlap ratio of adjacent cutting elements may range from about 0.05 to about 0.8 in some embodiments. For instance, in some embodiments the radial overlap ratio may range from a low of about 0.05, about 0.1, about 0.15, about 0.2, or about 0.25 to a high of about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, or more. For example, the radial overlap ratio may be between about 0.1 and about 0.5, between about 0.1 and about 0.3, or between about 0.05 and about 0.2.

The greater the radial overlap ratio, the greater the degree of overlap of a cutting element 110 in a first circumferential row (e.g., row 126) with another cutting element 110 in an adjacent second circumferential row (e.g., row 128). As this degree of overlap increases, it ma become easier for fractures created in the formation by the cutting elements 110 in the first circumferential row to communicate and connect with the fractures created in the formation by the cutting elements 110 in the adjacent second circumferential row. This communication between different fractures in the formation may make it easier to generate chips from the formation. Moreover, an increase in the degree of overlap may reduce the load on the set of cutting elements 110 that is responsible for the formation of these chips. U.S. Patent Application Publication No. 2009/0255735, which is assigned to the assignee of the present disclosure and is hereby incorporated by this reference in its entirety, further describes some aspects of the relationship between the fracture capability of one circumferential row of cutting elements to an adjacent circumferential row of cutting elements in a percussion hammer drill bit.

One or more conical cutting elements 142, 144, 146 may be disposed on the bit face 106 of the drill bit 100. In some embodiments, conical cutting elements 142, 144, 146 may be disposed in separate rows. Accordingly, although three rows of conical cutting elements 142, 144, 146 are shown in FIG. 1, more or fewer conical cutting elements 142, 144, 146 may be disposed on the bit face 106 of the drill bit 100 without departing from the scope of the present disclosure. Additionally, any of the conical cutting elements 142, 144, 146 (or a corresponding row thereof) may be disposed at least partially in or between any of the circumferential rows 126, 128, 130.

Thus, the first conical cutting element 142 may be disposed in the gage row 126, in the adjacent-to-gage row 128, or between the gage row 126 and the adjacent-to-gage row 128. The second conical cutting element 144 may be disposed in the adjacent-to-gage row 128, in the row 130, or between the adjacent-to-gage row 128 and the row 130. The third conical cutting element 146 may be disposed in the row 130, disposed in a more radially inner row of cutting elements, or between the row 130 and an inner row (or the axis 104).

The conical cutting elements 142, 144, 146 may have a conical or frustoconical shape. Such shape may be sharper or more pointed relative to SRT cutting elements (e.g., cutting elements 136, 138, 140). An outer surface of the conical cutting elements 142, 144, 146 may be oriented at an angle with respect to a longitudinal axis through the conical cutting element 142, 144, 146. In some embodiments, such an angle may range from about 15° to about 85°. For instance, the angle may range from a low of about 10°, about 15°, about 20°, about 25°, about 40°, or about 45° to a high of about 50°, about 55°, about 60°, about 65°, about 70°, about 75°, or more. For example, the angle may be between about 20° and about 40°, between about 10° and about 50°, or between about 40° and about 60°.

A crest portion of the conical cutting elements 142, 144, 146 may be sharp or flat. In some embodiments, the crest portion may have a radius of curvature that is less than the radius of curvature of the crest portion of the cutting elements 136, 138, 140. A ratio of the radius of curvature of the crest portion of the cutting elements 142, 144, 146 to the diameter of the cutting elements 142, 144, 146 may be between about 0.05:1 to about 0.5:1. For instance, the ratio of the radius of curvature of the crest portion to the diameter may range from a low of about 0.05:1, about 0.10:1, or about 0.15:1 to a high of about 0.20:1 about 0.25:1, about 0.30:1, or more. For example, the ratio of the radius of curvature to the diameter may be between about 0.12:1 and about 0.30:1 or between about 0.14:1 and about 0.25:1. According to one or more embodiments of the present disclosure, the conical cutting elements described herein may be similar to those described in U.S. patent application Ser. Nos. 61/441,319, 13/370,734, 61/499,851, and 13/370,862, all of which are assigned to the present assignee and are incorporated herein by this reference in their entireties.

Turning now to FIG. 2A, a profile view of a portion of a percussion hammer drill bit 200 is illustrated according to one or more embodiments of the present disclosure. The percussion hammer drill bit 200 may be similar or the same as the percussion hammer drill bit 100 disclosed with reference to FIGS. 1A and 1B. Thus, the discussion with respect to FIGS. 1A and 1B may be equally applicable to the embodiment illustrated in FIG. 2A.

The percussion hammer drill bit 200 may include a bit body 202 having a central bit axis 204 extending therethrough. The drill bit 200 may be indexed about the bit axis 204 during drilling operations. A bit face 206 may be disposed on an axial end portion of the bit body 202, and may include an inner region 212 and an outer region 214. In some embodiments, the inner region 212 may extend from the bit axis 204 to about 50% of an outermost radius 208 of percussion hammer drill bit 200. The outer region 214 may extend from the inner region 212 to the outermost radius 208 of the percussion hammer drill bit 200. In other embodiments, the inner region 212 may extend more or less than about 50% of the outermost radius 208 of the percussion hammer drill bit 200.

The inner region 212 may include a cone region 216, and the outer region 214 may include a shoulder region 218, a gage region 220, a skirt region 222, or some combination of the foregoing. The cone region 216 may include the radially innermost region of the drill bit 200 extending generally from the bit axis 204 to the shoulder region 218. The cone region 216 may have any suitable shape, and may be generally concave in some embodiments. In other embodiments, the cone region 216 may be generally convex, planar, otherwise shaped, or some combination of the foregoing. The shoulder region 218 may be positioned radially-outward from the cone region 216. The shoulder region 218 may be generally convex, generally convex, generally planar, or otherwise shaped, or have some combination of the foregoing. The gage region 220 may be positioned radially outward from the shoulder region 218, and the skin region 222 may be positioned radially outward from the gage region 220. The skirt region 222 may be generally parallel to the bit axis 204 in some embodiments.

The gage region 220 may include a circumferential gage row 226 having a plurality of gage cutting elements 236. The circumferential gage row 226 is the outermost radial row on the bit face 206, and where there are multiple gage cutting elements 236, they may be equally or unequally circumferentially offset from one another the gage row 226. The gage cutting elements 236 may be adapted to cut the corner of the borehole to maintain the diameter or gage of the borehole.

The shoulder region 218 may include a circumferential adjacent-to-gage row 228 having a second plurality of cutting elements (i.e., adjacent-to-gage cutting elements 238). The adjacent-to-gage cutting elements 238 may be equally or unequally circumferentially offset from one another in the adjacent to gage row 228 and positioned radially inward from the gage cutting elements 236 in the gage row 226. The adjacent-to-gage cutting elements 238 may be adapted to cut the bottom of the borehole in some embodiments.

The shoulder region 218 may also include one or more rows positioned radially inward from the adjacent-to-gage row 228 (see row 330 in FIG. 3A). The cone region 216 may include one or more rows 232 (e.g., three rows 232 a, 232 b, 232 c) positioned radially inward from the rows in the shoulder region 218, if any. The rows 232 may include a third plurality of cutting elements 240 (e.g., inner row cutting elements 240 a, 240 b, 240 c). The inner row cutting elements 240 may be adapted to gouge and remove formation material from the bottom of the borehole.

The cutting elements 236, 238, 240 may be SRT) cutting elements having a hemispherical shape. A ratio of the radius of curvature of the crest portion of the cutting elements 236, 238, 240 to the diameter of the cutting elements 236, 238, 240 may range from a low of about 0.3:1, about 0.4:1, or about 0.5:1 to a high of about 0.6:1, about 0.7:1, about 0.8:1, or more. For example, the ratio of the radius of curvature to the diameter may be between about 0.4:1 and about 0.7:1.

In at least one embodiment, the cutting elements 210 from different circumferential rows (e.g., rows 226, 228, 232) may be radially offset from one another with little to no overlap. In another embodiment, the cutting elements 210 from one circumferential row may at least partially radially overlap with the cutting elements 210 from a different circumferential row. The degree of radial overlap of the cutting elements 210 in adjacent circumferential rows may be characterized by the ratio of the radial overlap distance to the radial span distance of the overlapping cutting elements. The radial overlap ratio of adjacent cutting elements may range from a low of about 0.05, about 0.1, about 0.15, about 0.2, or about 0.25 to a high of about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, or more. For example, the radial overlap ratio may be between about 0.1 and about 0.5, between about 0.1 and about 0.3, or between about 0.05 and about 0.2.

The greater the radial overlap ratio, the greater the degree of overlap of a cutting element 210 in a first circumferential row (e.g., gage row 225) with another cutting element 210 in an adjacent second circumferential row (e.g., adjacent-to-gage row 228). As this degree of overlap increases, fractures created in the formation by the cutting elements 210 in the first circumferential row may more easily communicate and connect with the fractures created in the formation by the cutting elements 210 in the adjacent second circumferential row. This communication between different fractures in the formation may make it easier to generate chips from the earthen formation. Moreover, an increase in the degree of overlap may reduce the load on the set of cutting elements that is responsible for the formation of these chips.

Optionally, one or more conical cutting elements 242, 244, 246 may be disposed on the bit face 206 of the drill bit 200. In some embodiments, the conical cutting elements 242, 244, 246 may be disposed at different radial positions, such there are one or more first conical cutting elements 242, one or more second conical cutting elements 244, and one or more third conical cutting elements 246. Thus, although three conical cutting elements 242, 244, 246 are shown in FIG. 2A, more or less conical cutting elements may be disposed circumferentially around the corresponding bit face 206 of the drill bit 200 without departing from the scope of the present disclosure. Any of first, second, and third conical cutting elements 242, 244, 246 may be disposed at least partially in or between any of the circumferential rows 226, 228, 232.

The first, second, and third conical cutting elements 242, 244, 246 may have a conical or frustoconical shape as disclosed herein. In some embodiments, an outer surface of the conical cutting elements 242, 244, 246 may be oriented at an angle with respect to a longitudinal axis through the conical cutting element 242, 244, 246. The angle may range from a low of about 10°, about 15°, about 20°, about 25°, about 40°, or about 45° to a high of about 50°, about 55°, about 60°, about 65°, about 70°, about 75°, or more. For example, the angle may be between about 10° and about 40°, between about 20° and about 50°, or between about 40° and about 60°.

A crest portion of the conical cutting elements 242, 244, 246 may be sharp, flat, or curved. For instance, the crest portion may have a radius of curvature that is less than the radius of curvature of the crest portion of the cutting elements 236, 238, 240. A ratio of the radius of curvature of the crest portion of the cutting elements 242, 244, 246 to the diameter of the cutting elements 242, 244, 246 may range from a low of about 0.05:1, about 0.10:1, or about 0.15:1 to a high of about 0.20:1, about 0.25:1, about 0.30:1, or more. For example, the ratio of the radius of curvature to the diameter may be between about 0.12:1 and about 0.30:1 or between about 0.14:1 and about 0.25:1.

The first conical cutting element 242 may be disposed in the gage row 226, in the adjacent-to-gage row 228, or between the gage row 226 and the adjacent-to-gage row 228 (as shown). The second conical cutting element 244 may be disposed in the adjacent-to-gage row 228, in a row in the shoulder region 218, in one of the rows 232 in the cone region 216, between the adjacent-to-gage row 228 and a row in the shoulder region 218, or between the adjacent-to-gage row 228 (or other row in the shoulder region 218) and the rows 232 in the cone region 216 (as shown). The third conical cutting element 246 may be disposed in a row in the shoulder region 218, in one of the rows 232 in the cone region 216, between the adjacent-to-gage row 228 (or another row in the shoulder region 218) and the rows 232 in the cone region 216, or between rows 232 of the cone region 216 (as shown).

FIG. 2B depicts an enlarged, partial profile view of a cutting profile of the percussion hammer drill bit 200, according to one or more embodiments. Referring to FIGS. 2B and 2C, a cutting plane 211 may be in tangential contact with a crest portion 237 of the gage cutting elements 236 and a crest portion 239 of the adjacent-to-gage cutting elements 238. As used herein, “cutting plane” refers to a plane that is in tangential contact with the crest portions of two cutting elements in adjacent rows (e.g., rows 236, 238) or between the crest portions of two cutting elements in the same circumferential row.

As shown, a crest portion 243 of first conical cutting element 242 may be in tangential contact with the cutting plane 211. When the crest portion 243 of the first conical cutting element 242 is in tangential contact with the cutting plane 211, the first conical cutting element 242 may impact the formation at substantially the same time as the gage cutting elements 236 and the adjacent-to-gage cutting elements 238. As a result, the first conical cutting element 242 may create fractures in the formation at substantially the same depth as the gage cutting elements 236 and the adjacent-to-gage cutting elements 238.

Even when the crest portion 243 of the first conical cutting element 242 is in tangential contact with the cutting plane 211, the first conical cutting element 242 may create additional fractures in the formation that are capable of communicating with the fractures created in the formation by the gage cutting elements 236 and the adjacent-to-gage cutting elements 238. As a result, generating a chip from the formation may become easier when the crest portion 243 of the first conical cutting element 242 is in tangential contact with the cutting plane 211.

In at least one embodiment, the crest portion 243 of first conical cutting element 242 may be offset from the cutting plane 211. For example, the crest portion 243 of first conical cutting element 242 may extend beyond the cutting plane 211 by a distance 213. The distance 213 may range from about 1% to about 80% of the height of the first conical element 242 in some embodiments. For instance, the distance 213 may range from a low of about 1%, about 3%, about 5%, about 10%, or about 20% to a high of about 30%, about 40%, about 50%, about 60%, about 70%, or more of the total height of the first conical cutting element 242 as measured from the bit face 206. For example, the distance 213 may be up to about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70% or more of the total height of the first conical cutting element 242. The distance 213 may also be between about 1% and about 10%, between about 1% and about 20%, between about 10% and about 20%, or between about 3% and about 50% of the total height of the .first conical cutting element 242.

When the crest portion 243 of first conical cutting element 242 extends beyond the cutting plane 211 by the distance 213, the first conical cutting element 242 may pre-fracture the formation by impacting the formation before the gage cutting elements 236 and/or the adjacent-to-gage cutting elements 238. In addition, when the crest portion 243 of first conical cutting element 242 extends beyond the cutting plane 211 by the distance 213, the first. conical cutting element 242 may create a fracture in the formation that is deeper than the fractures created by the gage cutting elements 236/or and the adjacent-to-gage cutting elements 238. As such, the first conical cutting element 242 may create a deeper fracture contour or “groove” in the formation than that created by the gage cutting elements 236 andior the adjacent-to-gage cutting elements 238. This groove of pre-fractured formation material may facilitate the communication between the fractures created by the gage cutting elements 236 and the adjacent-to-gage cutting elements 238, thereby making it easier to generate chips from the formation during drilling operations. Moreover, this groove of pre-fractured formation material may provide a stress relieved area or a free face toward which the fractures created by the gage cutting. elements 236 and the adjacent-to-gage cutting elements 238 may easily propagate. As used herein, “free face” refers to an unconfined portion of the formation that provides room for the expansion and movement of fractured rock. The free face created by the first conical cutting element 242 may provide a stress relieved area that fractured rock may move toward, thereby using less energy for the fracture generation process.

In at least one embodiment, the crest portion 243 of first conical cutting element 242 may be below the cutting plane 211. For example, the crest portion 243 of first conical cutting element 242 may be below the cutting plane 211 by a distance 215. The distance 215 may range about 0.5% to about 50% of the total height of the first conical cutting element 242. For instance, the distance 215 may range from a low of about 0.5%, about 1%, about 2%, about 4%, or about 6% to a high of about 8%, about 10%, about 15%, about 20%, about 25%, or more of the total height of the first conical cutting element 242 as measured from the bit face 206. For example, the distance 215 may be between about 0.5% and about 3%, between about 1% and about 5%, or between about 1% and about 10%.

When the crest portion 243 of first conical cutting element 242 is below the cutting plane 211, the first conical cutting element 242 may not initially engage the formation during drilling. Rather, the first conical cutting element 242 may serve as a back-up to the gage cutting elements 236 and/or the adjacent-to-gage cutting elements 238, and the first conical cutting element 242 may engage the formation after the gage cutting elements 236 andlor the adjacent-to-gage cutting elements 238 have been subjected to substantial wear, thus lowering the cutting plane 211, or when impacted into the formation a distance that allows the first conical cutting element 242 to also contact the formation. In another embodiment, the first conical cutting element 242 may engage the formation after a substantial kerf develops between the gage row 226 and the adjacent-to-gage row 228 due to the formation being highly resistant to fracture.

FIG. 2C depicts an enlarged, partial profile view of a portion of a cutting profile of a percussion hammer drill bit 200, according to one or more embodiments of the present disclosure. A cutting plane 217 may be defined as being in tangential contact with the crest portion 239 of the adjacent-to-gage cutting elements 238 and the crest portion 241 of the inner row cutting elements 240 in a row 232. As shown, the crest portion 245 of the second conical cutting element 244 may be in tangential contact with the cutting plane 217. When the crest portion 245 of the second conical cutting element 244 is in tangential contact with the cutting plane 217, the second conical cutting element 244 may impact the formation at substantially the same time as the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240. As a result, the second conical cutting element 244 may create fractures in the formation at substantially the same depth as the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240.

Even when the crest portion 245 of second conical cutting element 244 is in tangential contact with the cutting plane 217, the second conical cutting element 244 may create additional fractures in the formation that are capable of communicating with the fractures created in the formation by the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240. As a result, generating a chip from the formation may become easier when the crest portion 245 of second conical cutting element 244 is in tangential contact with the cutting plane 217.

In at least one embodiment, the crest portion 245 of second conical cutting element 244 may be offset from the cutting plane 217. For example, the crest portion 245 of second conical cutting element 244 may extend beyond the cutting plane 217 by the distance 219. The distance 219 may range from about 1% to about 80% of the total height of the second conical cutting element 244. For instance, the distance 219 may range from a low of about 1%, about 3%, about 5%, about 10%, or about 20% to a high of about 30%, about 40%, about 50%, about 60%, about 70% or more of the total height of the second conical cutting element 244, as measured from the bit face 206. For example, the distance 219 may be up to about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, or more of the total height of the second conical cutting element 244. The distance 219 may also be between about 1% and about 10%, between about 1% and about 20%, between about 10% and about 20%, or between about 3% and about 50% of the total height of the second conical cuffing element 244.

When the crest portion 245 of second conical cutting element 244 extends beyond the cutting plane 217 by the distance 219, the second conical cutting element 244 may pre-fracture the formation by impacting the formation before the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240. In addition, when the crest portion 245 of second conical cutting element 244 extends beyond the cutting plane 217 by the distance 219, the second conical cutting element 244 may create a fracture in the formation that is deeper than the fractures created by the adjacent-to-gage cutting elements 238 andlor the inner row cutting elements 240. As such, the second conical cutting element 244 may create a deeper fracture contour or groove in the formation than that created by the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240. This groove of pre-fractured formation material may facilitate the communication between the fractures created by the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240, thereby making it easier to generate chips from the formation during chilling operations. Moreover, this groove of pre-fractured formation material may provide a stress relieved area or a free face toward which the fractures created h the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240 may easily propagate. The free face created by the second conical cutting element 244 may provide a stress relieved area that fractured rock may move toward, thereby using less energy for the fracture generation process.

In at least one embodiment, the crest portion 245 of second conical cutting element 244 may be below the cutting plane 217. For example, the crest portion 245 of second conical cutting element 244 may be below the cutting plane 217 by a distance 221. The distance 221 may range from about 0.5% to about 50% of the total height of the second conical cutting element 244 as measured from the bit face 206. For instance, the distance 221 may range from a low of about 0.5%, about 1%, about 2%, about 4%, or about 6% to a high of about 8%, about 10%, about 15%, about 20%, about 25% or more of the total height of the second conical cutting element 244. For example, the distance 221 may be between about 0.5% and about 3%, between about 1% and about 5%, or between about 1% and about 10%.

When the crest portion 245 of second conical cutting element 244 is below cutting plane 217, the second conical cutting element 244 may not initially engage the formation during drilling. Rather, the second conical cutting element 244 may serve as a back-up to the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240, and the second conical cutting element 244 may engage the formation after the adjacent-to-gage cutting elements 238 and/or the inner row cutting elements 240 have been subjected to substantial wear, thus lowering the cutting plane 217. In another embodiment, the second conical cutting element 244 may engage the formation after a substantial kerf develops between the adjacent-to-gage row 228 and the row 230 due to the formation being highly resistant to fracture, or when adjacent-to-gage cutting elements 238 and/or gage cutting elements 236 have penetrated the earthen formation to a depth allowing the second conical cutting element 244 to engage the formation.

FIG. 2D depicts an enlarged, partial profile view of a portion of a cutting profile of a percussion hammer drill bit 200, according to one or more embodiments of the present disclosure. A cutting plane 223 may be defined as being in tangential contact with the crest portions 241 of the inner row cutting elements 240 a in the row 232 a and the inner row cutting elements 240 b in the row 232 b. The inner row cutting elements 240 a, 240 b may each be in a cone region (e.g., cone region 216 of FIG. 2A) in some embodiments. In other embodiments, the inner row cutting elements 240 a, 240 b may be in different regions (e.g., cutting element 240 a may be in a shoulder region 218 while cutting element 240 b is in a cone region 216).

As shown, the crest portion 247 of the third conical cutting element 246 may be in tangential contact with the cutting plane 223. When the crest portion 247 of the third conical cutting element 246 is in tangential contact with the cutting plane 223, the third conical cutting element 246 may impact the formation at substantially the same time as the inner row cutting elements 240 a in the row 232 a and/or the inner row cutting elements 240 b in the row 232 b. As a result, the third conical cutting element 246 may create fractures in the formation at substantially the same depth as the inner row cutting elements 240 a in the row 232 a and/or the inner row cutting elements 240 b in the row 232 b.

Even when the crest portion 247 of third conical cutting element 246 is in tangential contact with the cutting plane 223, the third conical cutting element 246 may create additional fractures in the formation that are capable of communicating with the fractures created in the formation by the inner row cutting elements 240 a in the row 232 a and the inner row cutting elements 240 b in the row 232 b. As a result, generating a chip from the formation may become easier when the crest portion of third conical cutting element 246 is in tangential contact with the cutting plane 223.

In at least one embodiment, the crest portion 247 of third conical cutting element 246 may be offset from the cutting plane 223. For example, the crest portion 247 of third conical cutting element 246 may extend beyond the cutting plane 223 by a distance 225. In some embodiments, the distance 225 may range from about 1% to about 80% of the total height of the third conical cutting element 246, as measured from the bit face 206. For instance, the distance 225 may range from a low of about 1%, about 3%, about 5%, about 10%, or about 20% to a high of about 30%, about 40%, about 50%, about 60%, about 70% or more of the total height of the third conical cutting element 246. For example, the distance 225 may be up to about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70% or more of the total height of the third conical cutting element 246. The distance 225 may also be between about 1% and about 10%, between about 1% and about 20%, between about 10% and about 20%, or between about 3% and about 50% of the total height of the third conical cutting element 246.

When the crest portion 247 of third conical cutting element 246 extends beyond the cutting plane 223 by the distance 225, the third conical cutting element 246 may pre-fracture the formation by impacting the formation before the inner row cutting elements 240 a in the row 232 a (e.g., in a cone or shoulder region) and/or the inner row cutting elements 240 b in the row 232 b (e.g., in the cone or shoulder region). In addition, when the crest portion 247 of third conical cutting element 246 extends beyond the cutting plane 223 by the distance 225, the third conical cutting element 246 may create a fracture in the formation that is deeper than the fractures created by the inner row cutting elements 240 a in the row 232 a and/or the inner row cutting elements 240 b in the row 232 b. As such, the third conical cutting element 246 may create a deeper fracture contour or groove in the formation than that created by the inner row cutting elements 240 a and/or the inner row cutting elements 240 b. This groove of pre-fractured formation material may flicilitate the communication between the fractures created by the inner row cutting elements 240 a and the inner row cutting elements 240 b, thereby making it easier to generate chips from the formation during drilling operations. Moreover, this groove of pre-fractured formation material may provide a stress relieved area or a free face toward which the fractures created by the inner row cuffing elements 240 a and/or inner row cutting elements 240 b may easily propagate. The free face created by the third conical cutting element 246 may provide a stress relieved area that fractured rock may move toward, thereby using less energy for the fracture generation process.

In at least one embodiment, the crest portion 247 of third conical cutting element 246 may be below cutting plane 223. For example, the crest portion 247 of third conical cutting element 246 may be below the cutting plane 223 by a distance 227. In some embodiments, the distance 227 may range from about 0.5% to about 50% of the total height of the third conical cutting element 246 (as measured from the bit face 206). For instance, the distance 227 may range from a low of about 0.5%, about 1%, about 2%, about 4%, or about 6% to a high of about 8%, about 10%, about 15%, about 20%, about 25% or more of the total height of the third conical cutting element 246 (as measured from the bit face 206). For example, the distance 227 may be between about 0.5% and about 3%, between about 1% and about 5%, or between about 1% and about 10%.

When the crest portion 247 of third conical cutting element 246 is below cutting plane 223, the third conical cutting element 246 may not initially engage the formation during drilling. Rather, the third conical cutting element 246 may serve as a back-up to the inner row cutting elements 240 a in the row 232 a and/or the inner row cutting elements 240 b in the row 232 b, and the third conical cutting element 246 may engage the formation after the inner row cutting elements 240 a and/or the inner row cutting elements 240 b have been subjected to substantial wear, thus lowering the cutting plane 223. In another embodiment, the third conical cutting element 246 may engage the formation after a substantial kerf develops between the row 232 a and the row 232 b due to the formation being highly resistant to fracture, or when the depth of penetration of the cutting elements 240 a, 240 b allows the third conical cutting element 246 to contact the formation.

FIG. 3A depicts a partial profile view of a percussion hammer drill bit 300, and FIG. 3B depicts an enlarged, partial view of the percussion hammer drill bit 300 shown in FIG. 3A, according to one or more embodiments of the present disclosure. A bit face 306 may be disposed on an axial end portion of the bit body 302, and may include an inner region 312 and an outer region 314. In some embodiments, the inner region 312 may include a cone region 316, and the outer region 314 may include a shoulder region 318, a gage region 320, a skirt region 322, or some combination of the foregoing.

A conical cutting element 350 may be disposed at least partially within a circumferential gage row 326. The conical cutting element 350 is referred to herein as the gage conical cutting element 350. Because the gage conical cutting element 350 is disposed within circumferential gage row 326, the gage conical cutting element 350 is adjacent to the sidewall of the borehole (not shown). In this position, the gage conical cutting element 350 may be adapted to cut and fracture the gage portion of the borehole during drilling operations.

A cutting plane 311 may be defined to be in tangential contact with the crest portion 337 of adjacent gage cutting elements in the circumferential gage row 326. A crest portion 351 of gage conical cutting element 350 may also be in tangential contact with the cutting plane 311. When the crest portion 351 of the gage conical cutting element 350 is in tangential contact with the cutting plane 311, the gage conical cutting element 350 may impact the formation at substantially the same time as the gage cutting elements 336. As a result, the gage conical cutting element 350 may create fractures in the formation at substantially the same depth as the gage cutting elements 336. When the crest portion 351 of the gage conical cutting element 350 is in tangential contact with the cutting plane 311, the gage conical cutting element 350 may create additional fractures in the formation that are capable of communicating with the fractures created in the formation by the crest portion of the gage cutting elements 336. As a result, generating a chip from the formation may become easier when the gage conical cutting element 350 is in tangential contact with the cutting plane 311.

In at least one embodiment, the crest portion 351 of gage conical cutting element 350 may be offset from the cutting plane 311 (as shown). For example, the crest portion 351 of gage conical cutting element 350 may extend beyond the cutting plane 311 by a distance 329. In some embodiments, the distance 329 may range from about 1% to about 80% of the total eight of the gage conical cutting element 350, as measured from the bit face 306. For instance, the distance 329 may range from a low of about 1%, about 3%, about 5%, about 10%, or about 20% to a high of about 30%, about 40%, about 50%, about 60%, about 70% or more of the total height of the gage conical cutting element 350 (as measured from the bit face 306). In another example embodiment, the distance 329 may be up to about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70% or more of the total height of the gage conical cutting element 350. The distance 329 may also be between about 1% and about 10%, between about 1% and about 20%, between about 10% and about 20%, or between about 3% and about 50% of the total height of the gage conical cutting element 350.

When the crest portion 351 of gage conical cutting element 350 extends beyond the cutting plane 311 by the distance 329, the gage conical cutting element 350 may pre-fracture the formation by impacting the formation before some, and potentially each, gage cutting element 336. In addition, the gage conical cutting element 350 may create a fracture in the formation that is potentially deeper than the fractures created by the gage cutting elements 336. The gage conical cutting element 350 may pre-split the side and/or the bottom corner of the borehole, by creating a deeper fracture contour or groove in the formation than that created by the gage cutting elements 336. This groove of pre-fractured formation material may facilitate the communication between the fractures created by the gage cutting elements 336, thereby making it easier to generate chips from the formation during drilling operations. Moreover, this groove of pre-fractured formation material may provide a stress relieved area or a free face toward which the fractures created by the gage cutting elements 336 may easily propagate. The free face created by the gage conical cutting element 350 may provide a stress relieved area where fractured rock may move toward, thereby using less energy for the fracture generation process. In another embodiment, the gage conical cutting element 350 may be below the cutting plane 311 by a distance 331.

FIG. 4A depicts a profile view of a portion of a percussion hammer drill bit 400, and FIG. 4B depicts an enlarged, partial view of the percussion hammer drill bit 400 shown in FIG. 4A, according to one or more embodiments of the present disclosure. A bit face 406 may be disposed on an axial end portion of the bit body 402, and may include an inner region 412 and an outer region 414. In some embodiments, the inner region 412 may include a cone region 416, and the outer region 414 may include a shoulder region 418, a gage region 420, a skirt region 422, or some combination of the foregoing. A plurality of conical cutting elements 452 may be positioned or otherwise disposed on the bit face 406 of the drill bit 400. The conical cutting elements 452 may be positioned in one or more circumferential conical cutting element rows 453. The various rows 453 may be radially offset on the bit face 406.

The conical cutting elements 452 in a particular row 453 may be circumferentially offset from one another. The conical cutting elements 452 in a given row 453 may, in some embodiments, at least partially radially overlap with the conical cutting elements 452 in an adjacent row 453. Generally, the degree of overlap of the cutting profiles of overlapping conical cutting elements 452 in adjacent circumferential conical cutting rows 453 may be characterized by the ratio of the radial overlap distance to the radial span distance of the overlapping conical cutting elements, as described herein. According to one or more embodiments of the present disclosure, the radial overlap ratio of adjacent conical cutting elements 452 may range from about 0.05 to about 0.95. For instance, the radial overlap ratio may range from a low of about 0.05, about 0.1, about 0.15, about 0.2, or about 0.25 to a high of about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, or more. For example, the radial overlap ratio may be between about 0.1 and about 0.5, between about 0.1 and about 0.3, or between about 0.05 and about 0.2.

Each conical cutting element 452 in a given row 453 may at least partially radially overlap with a cutting element 410 in an adjacent circumferential row. Generally, the degree of overlap of the conical cutting elements 452 and the cutting elements 410 in adjacent circumferential conical cutting element rows 453 and circumferential cutting element rows 426, 428, 430, 432, respectively, may be characterized by the ratio of the radial overlap distance to the radial span distance of the overlapping conical cutting elements 452 and cutting elements 410, as described herein. According to one or more embodiments of the present disclosure, the radial overlap ratio of adjacent conical cutting elements 452 and cutting elements 410 may range from about 0.05 to about 0.9. For instance, the radial overlap ratio may range from a low of about 0.05, about 0.1, about 0.15, about 0.2, or about 0.3 to a high of about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, or more. For example, the radial overlap ratio may be between about 0.05 and about 0.4, between about 0.3 and about 0.6, or between about 0.4 and about 0.8.

The greater the radial overlap ratio of adjacent conical cutting elements 452 and cutting elements 410, the greater the degree of overlap of a conical cutting element 452 in a first circumferential row with a cutting element 410 in an adjacent second circumferential row. As this degree of overlap increases, it may become easier for fractures created in the formation by the conical cutting elements 452 in the first circumferential row to communicate and connect with the fractures created in the formation by the cutting elements 410 in the adjacent second circumferential row. This communication between different fractures in the formation may make it easier to generate chips from the formation. Moreover, an increase in the degree of overlap may reduce the load on the set of cutting elements that are responsible for the formation of these chips.

In at least one embodiment, the circumferential conical cutting element rows 453 may include a first circumferential conical cutting element row 454, a second circumferential conical cutting element row 456, and a third circumferential conical cutting element row 458. Although FIGS. 4A and 4B show three circumferential conical cutting element rows 454, 456, 458, between the circumferential gage row 426 and the circumferential adjacent-to-gage row 428, any number of conical cutting element rows 453 may be disposed between any adjacent circumferential rows 426, 428, 430, 432 without departing from the scope of the present disclosure.

In some embodiments, the circumferential conical cutting element rows 454, 456, 458 may be disposed between the circumferential gage row 426 and the circumferential adjacent-to-gage row 428. For example, the first circumferential conical cutting element row 454 may at least partially radially overlap with the gage cutting elements 436 in the circumferential gage row 426. Likewise, the third circumferential conical cutting element row 458 may at least partially radially overlap with the adjacent-to-gage cutting elements 438. In at least some embodiments, the second circumferential conical cutting element row 456 may at least partially radially overlap with the first and/or third circumferential conical cutting element rows 454, 458. The conical cutting element rows 454, 456, 458 between circumferential gage row 426 and circumferential adjacent-to-gage row 428 may provide more localized fracture of the bottom of the borehole than that provided by plurality of gage cutting elements 436 and plurality of adjacent-to-gage cutting elements 438 alone.

A cutting plane 411 may be defined as being in tangential contact with the crest portion 437 of the gage cutting elements 436 and the crest portion 439 of the adjacent-to-gage cutting elements 438. As shown, a crest portion 455 of the conical cutting element 452 in the first circumferential conical cutting element row 454 may be in about tangential contact with the cutting plane 411. When the crest portion 455 of the conical cutting element 452 in first circumferential conical cutting element row 454 is in tangential contact with the cutting plane 411, the conical cutting element 452 in first circumferential conical cutting element row 454 may impact the formation at substantially the same time as the gage cutting elements 436 and/or the adjacent-to-gage cutting elements 438. As a result, the conical cutting element 452 in the first circumferential conical cutting element row 454 may create fractures in the formation at substantially the same depth as the gage cutting elements 436 and the adjacent-to-gage cutting elements 438.

Even when the crest portion 455 of each conical cutting element 452 in first circumferential conical cutting element row 454 is in tangential contact with the cutting plane 411, the conical cutting element 452 in first circumferential conical cutting element row 454 may create additional fractures in the formation that are capable of communicating with fractures created in the formation by the gage cutting elements 436 and the adjacent-to-gage cutting elements 438. As a result, generating a chip from the formation may become easier.

The second circumferential conical cutting element row 456 and/or the third circumferential conical cutting element row 458 may be positioned adjacent to one another and between adjacent rows of cutting elements 410 (e.g., between the circumferential gage row 426 and the circumferential adjacent-to-gage row 428) to create additional fractures in the bottom of the borehole during drilling operations. A crest portion 457 of the conical cutting element 452 in the second circumferential conical cutting element row 456 and crest portion 459 of the conical cutting element 452 in the third circumferential conical cutting element row 458 may extend beyond the cutting plane 411 in sonic embodiments. For example, the crest portions 457, 459 may extend beyond the cutting plane by a distance 413. The distance 413 may range from a low of about 1%, about 3%, about 5%, about 10%, or about 20% to a high of about 30%, about 40%, about 50%, about 60%, about 70% or more of the total height of the conical cutting elements 452 in the second andlor third circumferential conical cutting element rows 456, 458 (as measured from the bit face 406). For example, the distance 413 may be up to about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, or more of the total height of the conical cutting elements 452 in the second and/or third circumferential conical cutting element rows 456, 458. The distance 413 may also be between about 1% and about 10%, between about 1% and about 20%, between about 10% and about 20%, or between about 3% and about 50% of the total height of the conical cutting elements 452 in the second and/or third circumferential conical cutting element rows 456, 458.

When the crest portions 457, 459 of conical cutting elements 452 in the circumferential conical cutting element row 456 and/or the third circumferential conical cutting element row 458 extend beyond the cutting plane 411, the conical cutting elements 452 in the second circumferential conical cutting element row 456 andlor the third circumferential conical cutting element row 458 may pre-fracture the formation by impacting the formation before the crest portion 437 of gage cutting elements 436 and/or the crest portion 439 of adjacent-to-gage cutting elements 438. In addition, the conical cutting elements 452 in the second circumferential conical cutting element row 456 and/or the third circumferential conical cutting element row 458 may create a fracture in the formation that is deeper than the fractures created by the gage cutting elements 436 and/or the adjacent-to-gage cutting elements 438.

The conical cutting elements 452 in the second circumferential conical cutting element row 456 and/or the third circumferential conical cutting element row 458 may pre-split the formation between circumferential gage row 426 and circumferential adjacent-to-gage row 428 by creating deeper fracture contours or grooves in the formation than that created by the gage cutting elements 436 and the adjacent-to-gage cutting elements 438. Because these grooves of pre-fractured formation material may be in close proximity to one another, these grooves may further facilitate the communication between the fractures created by the gage cutting elements 436 and the adjacent-to-gage cutting elements 438, thereby making it easier to generate chips from the formation during drilling operations. Moreover, these grooves of pre-fractured formation material may provide stress relieved areas or free faces toward which the fractures created by the gage cutting elements 436 and the adjacent-to-gage cutting elements 438 may easily propagate. The free faces created by the conical cutting elements 452 in the second circumferential conical cutting element row 456 and/or the third circumferential conical cutting element row 458 may provide a stress relieved area where fractured rock may move toward, thereby using less energy for the fracture generation process.

FIG. 5A depicts a profile view of a portion of a percussion hammer drill bit 500, and FIG. 5B depicts an enlarged, partial view of the percussion hammer drill bit 500 shown in FIG. 5A, according to one or more embodiments of the present disclosure. A bit face 506 may be disposed on an axial end portion of the bit body 502, and may include an inner region 512 and an outer region 514. In some embodiments, the inner region 512 may include a cone region 516, and the outer region 514 may include a shoulder region 518, a gage region 520, a skirt region 522, or some combination of the foregoing.

FIG. 5A shows plurality of conical cutting elements 552 disposed on a bit face 506. The conical cutting elements 552 may be disposed in one or more circumferential conical cutting element rows 553. For example, the conical cutting elements 552 may be disposed in a first circumferential conical cutting element row 554, a second circumferential conical cutting element row 556, and a third circumferential conical cutting element row 560.

In the illustrated embodiment, the circumferential conical cutting element rows 554, 556 may be disposed between the circumferential gage row 526 and the circumferential adjacent-to-gage row 528. The conical cutting elements 552 in circumferential conical cutting element row 554 may at least partially radially overlap the gage cutting elements 536 in circumferential gage row 526. Likewise, the conical cutting elements 552 in circumferential conical cutting element row 556 may at least partially radially overlap the adjacent-to-gage cutting elements 538 in circumferential adjacent-to-gage row 528. In addition, the conical cutting elements 552 in the circumferential conical cutting element row 554 may at least partially overlap with the conical cutting elements 552 in the circumferential conical cutting element row 556. The conical cutting elements 552 in circumferential conical cutting element rows 554, 556 may provide more localized fracture of the bottom of the borehole than that provided by plurality of gage cutting elements 536 and plurality of adjacent-to-gage cutting elements 538 alone.

In some embodiments, a circumferential conical cutting element row 560 may be disposed between the adjacent-to-gage row 528 and a circumferential row 530 in a shoulder region 518. The conical cutting elements 552 in the circumferential conical cutting element row 560 may at least partially radially overlap the adjacent-to-gage cutting elements 538 in circumferential adjacent-to-gage row 528. Likewise, the conical cutting elements 552 in the circumferential conical cutting element row 560 may at least partially radially overlap the inner row cutting elements 540 in row 530. The conical cutting elements 552 in conical cutting element row 560 may provide more localized fracture of the borehole bottom than that provided by plurality of adjacent-to-gage cutting elements 538 and plurality of inner row cutting elements 540 row 530 alone.

A cutting plane 511 may be defined to be in tangential contact with the crest portion 537 of the gage cutting elements 536 and/or the crest portion 539 of the adjacent-to-gage cutting elements 538. As shown, a crest portion 555 of the conical cutting elements 552 in the first circumferential conical cutting element row 554 and a crest portion 557 of the conical cutting elements 552 in the second circumferential conical cutting element row 556 may be offset from the cutting plane 511 by a distance 513. The distance 513 may range from a low of about 1%, about 3%, about 5%, about 10%, or about 20% to a high of about 30%, about 40%, about 50%, about 60%, about 70% or more of the total height of the conical cutting elements 552 in the first and/or second circumferential conical cutting element rows 554, 556 (as measured from the bit face 506). For example, the distance 513 may be up to about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, or more of the total height of the conical cutting elements 552 in the first and/or second circumferential conical cutting element rows 554, 556. The distance 513 may also be between about 1% and about 10%, between about 1% and about 20%, between about 10% and about 20%, or between about 3% and about 50% of the total height of the conical cutting elements 552 in the first and/or second circumferential conical cutting element rows 554, 556.

When the crest portions 555, 557 of the conical cutting elements 552 in the first and/or second circumferential conical cutting element rows 554, 556 extend beyond the cutting plane 511, the conical cutting elements 552 in first circumferential conical cutting element row 554 and/or in second circumferential conical cutting element row 556 may pre-fracture the formation by impacting the formation before the crest portion of the gage cutting elements 536 and/or the adjacent-to-gage cutting elements 538. In addition, the conical cutting elements 552 in the first circumferential conical cutting element row 554 and the second circumferential conical cutting element row 556 may create a fracture in the formation that is deeper than the fractures created by the crest portion of the gage cutting elements 536 and the adjacent-to-gage cutting elements 538.

The conical cutting elements 552 in the first circumferential conical cutting element row 554 and/or the second circumferential conical cutting element row 556 may pre-split the formation between the circumferential gage row 526 and the circumferential adjacent-to-gage row 528 by creating deeper fracture contours or grooves in the formation than that created by the crest portion of the gage cutting elements 536 and/or the adjacent-to-gage cutting elements 538. Because these grooves of pre-fractured formation material may be in close proximity to one another, these grooves may further facilitate the communication between the fractures created by the crest portion of the gage cutting elements 536 and/or the adjacent-to-gage cutting elements 538, thereby making it easier to generate chips from the formation during drilling operations. Moreover, these grooves of pre-fractured formation material may provide stress relieved areas or free faces toward which the fractures created by the gage cutting elements 536 and/or the adjacent-to-gage cutting elements 538 may easily propagate. The free faces created b the conical cutting elements 552 in the first circumferential conical cutting element row 554 and/or the second circumferential conical cutting element row 556 may provide a stress relieved area that fractured rock may move toward, thereby using less energy for the fracture generation process.

A cutting plane 517 may be defined in tangential contact with the crest portion 539 of the adjacent-to-gage cutting elements 538 and the crest portion 541 of the inner row cutting elements 540. A crest portion 561 of the conical cutting elements 552 in the third circumferential conical cutting element row 560 may be in tangential contact with the cutting plane 517. When the crest portion 561 of the conical cutting elements 552 in third circumferential conical cutting element row 560 is in tangential contact with the cutting plane 517, the conical cutting elements 552 in the third circumferential conical cutting element row 560 may impact the formation at substantially the same time as the adjacent-to-gage cutting elements 538 and/or the inner row cutting elements in 540 in row 530. In addition, the conical cutting elements 552 in the third circumferential conical cutting element row 560 may create fractures in the formation at substantially the same depth as the adjacent-to-gage cutting elements 538 and the inner row cutting elements 540 in row 530.

The conical cutting elements 552 in the third circumferential conical cutting element row 560 may create additional fractures in the formation that are capable of communicating with fractures created in the formation by the crest portion of the adjacent-to-gage cutting elements 538 and/or the inner row cutting elements 540 in row 530. As a result, generating a chip from the formation may become easier when the conical cutting elements 552 in the third circumferential conical cutting element row 560 are in tangential contact with the cutting plane 517.

Referring generally now to FIGS. 1-5B, in operation, a drill bit (e.g., percussion hammer drill bit 100, 200, 300, 400, 500) may be run into a borehole on a work string until the drill bit contacts the bottom portion of the borehole. The drill bit may then moves hack and forth axially within the borehole, contacting the bottom portion of the borehole on each forward stroke. More particularly, the cutting elements and conical cutting elements on the drill bit may contact the bottom portion of the borehole on each forward stroke, thereby cutting or grinding the formation to extend the length of the borehole. In addition, the drill bit may be indexed between seine or each axial impact of the drill bit with the formation so that with each subsequent forward stroke, the cutting elements and conical cutting elements may contact different locations of the formation on the bottom portion of the borehole. The outer surface of the cutting elements and/or the conical cutting elements may be made of or include tungsten carbide, tungsten carbide with a super-abrasive material surface such as polycrystalline diamond (“PCD”) or cubic boron nitride (“PCBN”), other matrix materials of carbides, nitrides, or borides, or other materials, or any combination of the foregoing.

As used herein, the terms “inner” and “outer;” “up” and “down;” “upper” and “lower;” “upward” and “downward;” “above” and “below;” “inward” and “outward” and other like terms as used herein refer to relative positions to one another and are not intended to denote a particular direction or spatial orientation. The terms “couple,” “coupled,” “connect,” “connection,” “connected,” “in connection with,” and “connecting” refer to “in direct connection with” or “in connection with via another element or member.” The terms “hot” and “cold” refer to relative temperatures to one another. Where a range of values is provided, any two numbers listed may provide a range for embodiments of the present disclosure.

Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the scope of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of this disclosure. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §120, ¶ 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function. 

What is claimed is:
 1. A percussion drill bit for drilling a borehole, comprising: a bit body having a bit face; first and second cutting elements on the bit face, the first and second cutting elements defining a cutting plane in tangential contact with a crest portion of each of the first and second cutting elements; and a conical cutting element on the bit face and positioned at least partially between the first and second cutting elements, the conical cutting element having a crest portion offset from the cutting plane.
 2. The percussion drill bit of claim 1, the crest portion of the conical cutting element extending beyond the cutting plane by a distance up to about 70% of a total height of the conical cutting element as measured from the bit face.
 3. The percussion drill bit of claim 1, the crest portion of the conical cutting element being below the cutting plane by a distance up to about 25% of a total height of the conical cutting element as measured from the bit face.
 4. The percussion drill bit of claim 1, the first and second cutting elements being semi-round top cutting elements.
 5. The percussion drill bit of claim 1, the first and second cutting elements being at least partially conical.
 6. The percussion drill bit of claim 1, a radius of curvature of the crest portion of the conical cutting element being less than a radius of curvature of the crest portions of the first and second cutting elements.
 7. The percussion drill bit of claim 1, the first and second cutting elements being circumferentially offset from one another.
 8. The percussion drill bit of claim 7, the first and second cutting elements being positioned in a circumferential gage row on the bit face.
 9. The percussion drill bit of claim 1, the first and second cutting elements being in first and second circumferential rows of cutting elements, respectively, the first circumferential row of cutting elements being radially outward relative to the second circumferential row of cutting elements.
 10. The percussion drill bit of claim 1, at least one of the first, second, or conical cutting elements comprising diamond.
 11. A percussion drill bit for drilling a borehole, comprising: a bit body having a bit face; first and second semi-round top cutting elements in an outer circumferential row on the bit face, the first and second semi-round top cutting elements defining a cutting plane in tangential contact with a crest portion of the first cutting element and a crest portion of the second cutting element; and a third cutting element on the bit face at least partially overlapping the outer circumferential row, the third cutting element being at least partially conical, and a crest portion of the third cutting element extending beyond the cutting plane by a distance up to about 70% of a total height of the third cutting element as measured from the bit face.
 12. The percussion drill bit of claim 11, a radius of curvature of the crest portion of the third cutting element being less than a radius of curvature of the crest portions of the first and second cutting elements.
 13. The percussion drill bit of claim 12, a ratio of the radius of curvature of the crest portion of the third cutting element to a diameter of the third cutting element being between about 0.12:1 and about 0.30:1 and a ratio of a radius of curvature of the crest portion of the first and second cutting elements to a diameter of the first and second cutting elements being between about 0.4:1 and about 0.7:1.
 14. The percussion drill bit of claim 11, at least one of the first, second, or third cutting elements comprising diamond.
 15. The percussion drill bit of claim 11, the outer circumferential row being a gage row.
 16. A method for drilling a borehole, comprising: running a percussion hammer drill bit into a borehole, the percussion hammer drill bit including: a bit body having a bit face; first and second cutting elements on the bit face and defining a cutting plane in tangential contact with a crest portion of the first cutting element and a crest portion of the second cutting element; and a third cutting element on the bit face and positioned at least partially between the first and second cutting elements, the third cutting element being at least partially conical and a crest portion of the third cutting element being offset from the cutting plane; and contacting a formation with the first, second, and third cutting elements to extend the borehole.
 17. The method of claim 16, wherein contacting the formation comprises: moving the bit body back and forth axially within the borehole; and indexing the bit body about a longitudinal axis extending therethrough.
 18. The method of claim 16, wherein the first and second cutting elements are: in a same circumferential gage row on the bit face; or in different circumferential rows on the bit face.
 19. The method of claim 16, wherein the crest portion of the third cutting element extends beyond the cutting plane by a distance up to about 70% of a total height of the third coning element as measured from the bit face.
 20. The method of claim 16, wherein the crest portion of the third cutting element is below the cutting plane by a distance up to about 25% of a total height of the third cutting element as measured from the bit face. 